Is it possible to divide text object horizontally, while retaining edit ability?
Sure but you would have to convert it into another form.
If you Convert > Mesh then you cannot edit the text.
If you use the scene output then it becomes an image that you can modify in the compositor (or in the VSE but the tools are not as complete)


Set up a camera to look at the text, I have used a shadeless material. Remember to set scene property to render alpha not sky.

Add scene node to compositor (use another scene if you like). Then split the same input into 2 with a crop node. Move them separately with a Translate node.